The present invention relates to the field of angioplasty. In particular, the present invention relates to a dilatation balloon catheter of the "over-the-wire" type having a relatively short distal guide wire lumen extending through the balloon of the catheter.
Angioplasty procedures have gained wide acceptance in recent years as efficient and effective methods for treating types of vascular disease. In particular, angioplasty is widely used for opening stenoses in the coronary arteries, although it is also used for the treatment of stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Typically, a hollow guide catheter is used in guiding the dilatation catheter through the vascular system to a position near the stenoses (e.g., to the coronary artery ostia). Using fluoroscopy, the physician guides the dilatation catheter the remaining distance through the vascular system until a balloon is positioned to cross the stenoses. The balloon is then inflated by supplying fluid under pressure through an inflation lumen in the catheter to the balloon. The inflation of the balloon causes stretching of the artery and pressing of the lesion into the artery wall, to reestablish acceptable blood flow through the artery.
There has been a continuing effort to reduce the profile and shaft size of the dilatation catheter so that the catheter not only can reach but also can cross a very tight stenosis. A successful dilatation catheter must also be sufficiently flexible to pass through tight curvatures, especially in the coronary arteries. A further requirement of a successful dilatation catheter is its "pushability". This involves the transmission of longitudinal forces along the catheter from its proximal end to its distal end so that a physician can push the catheter through the vascular system and the stenoses.
Two commonly used types of dilatation catheters are referred to as "over-the-wire" catheters and "non-over-the-wire" catheters. An over-the-wire catheter is one in which a separate guide wire lumen is provided in the catheter so that a guide wire can be used to establish the path through the stenoses. The dilatation catheter can then be advanced over the guide wire until the balloon on the catheter is positioned within the stenoses. One problem with the over-the-wire catheter is the requirement of a larger profile and a generally larger outer diameter along the entire length of the catheter in order to allow for a separate guide wire lumen therethrough.
A non-over-wire catheter acts as its own guide wire, and thus there is no need for a separate guide wire lumen. One advantage of a non-over-the-wire catheter is its potential for a reduced outer diameter along its main shaft since no discrete guide wire lumen is required. However, one disadvantage is the inability to maintain the position of the guide wire within the vascular system when removing the catheter and exchanging it for a catheter having a smaller (or larger) balloon diameter. Thus, to accomplish an exchange with a non-over-the-wire catheter, the path to the stenoses must be reestablished when replacing the catheter with one having a different balloon diameter.
In an effort to combine the advantages of an over-the-wire catheter with a non-over-the-wire catheter, catheters have been developed which have guide wire lumens which extend from a distal end of the catheter through the dilatation balloon and then exit the catheter at a point proximal of the dilatation balloon. The guide wire thus does not extend through the entire length of the catheter and no separate guide wire lumen is required along a substantially proximal section of the catheter. That proximal section can thus have a smaller outer diameter since it is only necessary to provide an inflation lumen therethrough for catheter operation. A further advantage of this type of modified over-the-wire catheter is that the frictional forces involved between the guide wire and the shortened guide wire lumen are reduced, thereby reducing resistance to catheter pushability and enhancing the "feel" and responsiveness of the catheter to a physician.
Perhaps the most significant advantage of using a shortened guide wire lumen is in the ease of exchange of the catheter over the guide wire. In performing an angioplasty procedure using such a catheter, the catheter is "back loaded" over the guide wire by inserting the proximal tip of the guide wire into a distal opening of the guide wire lumen in the catheter. The catheter is then advanced by "feeding" the catheter distally over the guide wire while holding the guide wire stationary. The proximal end of the guide wire will then emerge out of the proximal opening of the guide wire lumen (which is substantially spaced distally from the proximal end of the catheter itself) and is accessible again for gripping by the physician. The catheter can be preloaded onto the guide wire in this manner before the guide wire is inserted into the guide catheter or after. In either case, the guide wire is steered and passed through the guide catheter, coronary vessels and across a lesion. The exposed portion of the guide wire is then grasped while the catheter is advanced distally along the guide wire across the lesion. Using this procedure, little axial movement of the guide wire occurs during catheter loading and positioning for angioplasty.
If the dilatation balloon is found to be inadequate (too small or too large), the catheter can be similarly withdrawn without removing the guide wire from across the lesion. The guide wire is grasped while the catheter is withdrawn, and when the proximal opening of the guide wire lumen is reached, the grasping hand must be moved incrementally away from the proximal opening as the catheter is incrementally withdrawn, until the catheter is fully removed from the guide catheter and the guide wire is thus again exposed and accessible adjacent to the proximal end of the guide catheter.
This shortened guide wire lumen type of dilatation catheter design thus offers the advantages associated with the rapid exchangeability of catheters. The design also presents the potential to provide a smaller catheter shaft, since the guide wire is not contained within the proximal portion of the catheter shaft. The smaller catheter shaft thus allows for better contrast media injection and, as a result, better visualization. In addition, because of the rapid exchangeability features, standard non-extendable guide wires of approximately 175 centimeters in length may be used. Further, because the guide wire is contained in only a distal shorter guide wire lumen of the catheter, free wire movement is enhanced when compared to a standard over-the-wire catheter where the guide wire extends through a guide wire lumen extending along the entire length of the catheter.
While several structures for such shortened guide wire lumen dilatation catheter have been proposed these structures suffer from several disadvantages. Such catheters have been one piece polyethylene catheters having dual lumen configurations adjacent their distal regions. Typically, such catheters have larger than necessary shaft sizes and are stiffer in their distal regions than would be desired, including those portions bearing the dilatation balloon. A further disadvantage is that the proximal shaft portion of such catheters is relatively flexible, and has low column strength shaft, so that it tends to "bunch" and buckle when advanced across a lesion. To counteract this deficiency in such designs, additional stiffener elements have been provided in the shaft, which necessarily require a larger catheter shaft to accommodate the stiffener element structure. The known dilatation balloon catheter designs which include shortened guide wire lumens extending through the distal portion of the catheter suffer from the disadvantages mentioned above and do not take advantage of the unique opportunities presented by the possibilities of such designs in construction and application.